The present invention relates to an ultrasonic transducer as a main component of an ultrasonic probe of an ultrasonic apparatus such as an ultrasonic diagnostic apparatus and a method of manufacturing the same and, more particularly, to a two-dimensional array type ultrasonic transducer in which transducer elements for reversibly converting an electrical signal and an ultrasonic signal are arrayed in a matrix (two-dimensionally) and a method of manufacturing the same.
Various apparatuses using ultrasonic waves are widely used in the field of medicine. Of these apparatuses using ultrasonic waves, the most extensively used is an ultrasonic diagnostic apparatus which obtains tomographic images of soft tissues of living bodies by using the ultrasonic pulse reflection method. This ultrasonic diagnostic apparatus is known as a noninvasive method and displays a tomographic image of a tissue. Compared to other diagnostic apparatuses such as an X-ray diagnostic apparatus, an X-ray computer tomographic apparatus, a magnetic resonance imaging apparatus, and a nuclear medicine diagnostic apparatus, an ultrasonic diagnostic apparatus has the advantages that it can display images in real time, is small and inexpensive, has high safety with no exposure to X-rays, and is capable of blood flow imaging by using the ultrasonic Doppler method.
For these reasons, ultrasonic diagnostic apparatuses are extensively used in examinations of hearts, abdomens, mammary glands, and urinary organs, and in obstetrics and gynecology. Also, an ultrasonic diagnostic apparatus can display, e.g., heart beats and the motions of an unborn child in real time with a simple operation of bringing an ultrasonic probe into contact with the body surface, and can allow repetitive examinations because of its high safety. Additionally, examinations can be readily performed even on the bedside.
To generate a tomographic image of the interior of an object to be examined, an ultrasonic diagnostic apparatus scans an internal section of the object via an ultrasonic probe. This scan is classified into two types in accordance with the principle of scanning: one is mechanical scan by which an ultrasonic transducer is mechanically moved, and the other is electronic scan which uses electronic switching and delay control of arrayed transducer elements. The scan is also classified into two other types in accordance with the range of scanning: one is two-dimensional scan which scans a section with an ultrasonic beam, and the other is three-dimensional scan which scans an internal three-dimensional region of an object with an ultrasonic beam. The currently most frequently used three-dimensional scan is to translate or axially rotate, a two-dimensional scan type ultrasonic probe either manually or mechanically.
Since this three-dimensional scan requires a long scanning time, the time resolution of the scan is low, so the scan is impractical. To improve the time resolution, it is essential to use a two-dimensional array type ultrasonic probe in which a plurality of transducer elements are arrayed in a matrix and to scan a three-dimensional region electronically by using electronic switching and delay control of these transducer elements.
In the manufacture of a two-dimensional array type ultrasonic transducer to be incorporated into this two-dimensional array type ultrasonic probe, one of the most difficult problems to solve is a method of extracting leads from transducer elements arrayed at fine pitches.
One example is a method by which a conductor pad array formed in a matrix on the surface of a printed board is adhered to a discrete electrode array of transducer elements. Methods of electrically connecting the conductor pads on a printed board to the discrete electrodes of the transducer elements are: (1) a method using a conductive adhesive; (2) a method of heating, under pressure, an anisotropic conductive film sandwiched between the conductor pad array and the discrete electrode array of the transducer elements; and (3) a method of contact-bonding metal bumps formed on the conductor pads and on the discrete electrodes.
Unfortunately, in the method (1) the interval between the transducer elements must be increased in order to avoid conduction between adjacent discrete electrodes. Also, the methods (2) and (3) have the problems of, e.g., breakage of the transducer elements, depolarization (polarization shift) of the transducer elements heated in the connecting operation, and thermal deformation of the printed board, since these methods require pressing and/or heating. Further, these methods (1) to (3) have the common problem that the acoustic characteristics (wavelength, frequency band) of the ultrasonic transducer itself degradate in accordance with the acoustic characteristics of the printed board directly adhered to the transducer elements.
Furthermore, in the case the transducer plate is divided to obtain the transducer element array after the transducer plate is sticked on the printed circuit board, wiring on the printed circuit board are breaked. Therefore the element array after is defective in division.
To solve these problems, a method of burying a plurality of leads in a backing layer is being studied. In this method, elements certainly are separated to each other by gaps attained to the backing layer. However, the yield is low because the alignment of the leads with the discrete electrodes is not easy.